The present invention relates to apparatus and methods for feeding cellulosic chips into a chip container and simultaneously preventing the escape of gas from the container through the feed opening.
In modern continuous digesters, cellulosic chips and chemicals are fed to a digester where pulping reactions take place necessary to the production of pulp. The chips are usually pretreated in a steaming bin or vessel, typically by dirty steam recovered from the digester. Conventionally, chips are supplied the presteamer for a hopper or directly from a conveyor belt by a low pressure feeder. Such low pressure feeders are generally of a type provided with a star wheel wherein the pockets of the star wheel transport chips from the hopper or conveyor belt into the presteaming vessel. As those familiar with this art will appreciate, the atmosphere within the presteaming vessel is replete with and permeated by odorous sulfur compounds. Because of the potential for environmental and other poblems, it is desirable and almost essential to confine this gas within the pulping system so that any emissions from the system would be marginal or eliminated.
As a specific example of such problem in those systems using low pressure feeders of the star wheel type, the pockets in the star wheel feeder, of course, transport or pump chips into the presteaming vessel. However, those same pockets, when empty of chips, transport gas from the vessel through the inlet to the surrounding environment. That is, the conventional star wheel-type feeder, in operation, also serves as a pump which pumps gas from the vessel into the atmosphere. Notwithstanding efforts to provide feeders of this type with seals, the feeder itself causes undesirable gaseous emissions through this pumping action.
It is important also that the presteaming bin or vessel be maintained under a vacuum pressure. Conventional systems for feeding vessels of this type also admit substantial inlet air. This has required condensers, eductors, fans, piping and the like of substantial capacity in the system. The cost of this equipment is almost directly proportional to the quantity of air flowing into the bin and which must be exhausted via a containment and treatment system. It is therefore desirable to provide a presteaming vessel feeding system which minimizes or eliminates air flow into the vessel such that only a minimum quantity of air is removed from the vessel to maintain it under vacuum pressure.
An additional problem residing with prior feeders for steaming vessels is that the inlets are open substantially at the highest point in the steaming vessel where the noxious odorous gas collects. Thus, any opening of the feed inlet in that area necessarily results in egress of this foul smelling steam or gas from the vessel. It would therefore be highly desirable to locate the chip inlet feed opening at such other location as to preclude escape of this noxious odorous gas or steam.
According to the present invention, there is provided apparatus and methods for feeding cellulosic chips into a vessel, for example a presteaming vessel for use in pulp digesters, and for substantially precluding or minimizing the egress of noxious odorous gas and steam from the presteaming vessel when the chips are fed to the vessel. In accordance with the present invention, there is provided an upstanding, generally cylindrical vessel having a chip feed inlet through its upper surface. In a preferred form of the present invention, the inlet constitutes a rectangular walled tube which extends into the vesel and below its upper surface, terminating at its lower end at a pair of pivoted gates. The gates essentially comprise flat plates which are angled toward one another to provide a central opening through which chips may fall into the vessel. The gates are pivoted about horizontal, spaced parallel axes defined by horizontally extending parallel shafts which straddle the walled inlet within the vessel. The shafts extend outwardly through the walls of the vessel, terminating in counterweights on the opposite sides of the axes from the gates. In this form of the present invention, the gates and counterweights are constructed to pivot the shafts about the axes to equilibrium positions in which, in the absence of chips on the gates, the gates close the inlet.
When operating the feed system of the present invention, the chips are supplied by a conveyor belt to the inlet and deposited onto the gates. The weight of the chips on the gates cause the gates to move away from one another, forming an opening into the vessel. The chips thus fall through the inlet opening into the vessel simultaneously as they are being replenished from the supply conveyor belt. A level of chips on the gates in maintained such that the openings between the gates and between the gates and the margins of the chute are substantially occluded by the chips. In this manner, escape of gas from the vessel through the inlet is substantially prevented by the supply of chips on the gates above the opening as the chips are simultaneously fed into the vessel.
In another embodiment of the present invention, the gates are positively controlled by a fluid actuator. For example, the shafts external of the vessel may be provided with gear wheels which cooperate with a pair of idler gear wheels and a ratchet. The ratchet is under the control of a fluid-actuated cylinder. By actuating the cylinder and hence linearly displacing the ratchet, the shafts and, hence, gates, are rotated to open or close the inlet.
In another preferred form of the present invention, the walled inlet extends into and below the upper surface of the vessel. Consequently, the noxious odorous gas or steam which collects in the vessel collects substantially above the lower end of the inlet. Thus, the opening of the inlet into the vessel is at an elevation below the level of steam or gas in the vessel and such steam or gas would therefore not escape into the atmosphere through the chip feed opening.
In a still further preferred form of the present invention, the inlet may be provided with a feeder, for example of the star wheel type. The feeder may be located in the inlet upstream of the gates.
In a still further form of the present invention, two pairs of serially arranged gates are provided in the inlet chute. As a result, noxious, odorous gas or steam which may escape past the first gate closure is trapped by the second gate.
Therefore, in accordance with a preferred embodiment of the present invention, there is provided apparatus for feeding cellulosic chips comprising a vessel for receiving the chips and means carried by the vessel defining an inlet to the vessel for supplying chips thereto while simultaneously substantially precluding escape of gas from the container through the opening including means for supporting the chips in said inlet in positions substantially precluding escape of gas through the inlet while the chips are simultaneously supplied to the vessel.
In accordance with another preferred embodiment of the present invention, there is provided a method for feeding cellulosic chips into a vessel having an inlet and substantially simultaneously curtailing escape of odorous gas from the vessel through the inlet, comprising the steps of flowing the chips through the inlet into the vessel and simultaneously maintaining a mass of chips in the inlet at a predetermined level sufficient to occlude the inlet thereby to substantially preclude escape of gas from the vessel through the inlet.
Accordingly, it is a primary object of the present invention to provide novel and improved apparatus for feeding cellulosic chips into a vessel and simultaneously precluding or minimizing the escape of noxious odorous gas from the vessel.
These and further objects and advantages of the present invention will become more apparent upon reference to the following specification, appended claims and drawings.